Evolution Diary

Sex-based differences are the driving force behind the great diversity of colorful lizards on Caribbean islands, a new study says.

Scientists studying Anolis species on the islands of Cuba, Hispanola, Jamaica, and Puerto Rico say both the physical and behavioral differences between males and females probably sparked the development of new niche species as the reptiles evolved on their respective islands.

Reporting in the current issue of the journal Nature, researchers say their findings show for the first time that such differences can spur the evolution of new species.

“We looked at males and females [in] multiple species, and we found that females and males do things differently,” said lead study author, Marguerite A. Butler, an evolutionary biologist at the University of Hawai’i at Manoa.

In some Anolis species, she explained, males and females occupy different habitats and can have different features.

In Caribbean species, females have more toe pads for climbing and are generally smaller, denser, and longer than males.

“We’re suggesting that you can have diversity … between species or between sexes,” Butler said.

“So especially when you colonize a new place it might be that sexual dimorphism—differences between the sexes—is very great and that over time a speciation [a formation of a new species] occurs,” she said.

“It may actually be an important thing that’s occurring all the time.”

Sex, Looks, and Competition

Harvard University evolutionary biologist Jonathan B. Losos and Washington University mathematician Stanley A. Sawyer joined Butler on the study.

Losos suggested that the sexes may take on different characteristics to help the species make better use of its environment.

“[One] explanation is that sexual differences arise so that the sexes can utilize different resources and not compete with each other,” Losos said in a media statement.

“In some hummingbirds, for example, the sexes differ in the length of their beaks, allowing each to drink nectar from different flowers. By diverging in their resource use, the population as a whole can reach higher levels.”

Throughout the Caribbean, there are nearly 400 species of Anolis lizards, the most of any animal genus. In some species, males are territorial and maintain harems of females. In others, males and females nest communally.

Among other traits, the reptiles are distinguished by their preferred habitats and means of getting around.

Some lizards live on tree trunks near the ground and have long legs—better for running fast and jumping high.

Others live on the branches of shrubs and have short legs.

Story reposted from National Geographic